Vinylacetylene purification



Aug. 14, 1945. c K BUELL VINYLACETYLENE PURIFICATION Filed Dec. 9, 1945 BOLVNOLLDVHi Dumm ATTORNEYS v retenes Aug. i4, 194s 2,332,603 vnvmcarrmnu Punmca'rron Charles Keith Buell, Bunavlsta, Tex., assigner to Phillips Petroleumy Company, a corporation of Delaware Application December e, 194s, sel-n.1 No. 5513.609

(ci. 2oz-42) 7 Claims.

This invention relates to a method for recovering vinylacetylene from a complex hydrocarbon mixture containing the same. More specically, this invention relates to an improved method for recovering vinyiacetylene from a complex hydrocarbon mixture containing the same and also con taining butenes-2 and any or all of the other aliphatio C4 acetylenes, dioleilns, olens or paralns generally encountered in Petroleum processes.

Acetylenes appear in small quantities in the reaction products of certain thermal cracking and catalytic dehydrogenation processes. The C4 acetylenes, namely vinylacetylene, ethylacetylene, bi-acetylene, and dimethylacetylene are of such volatility that they will be concentrated in the C4 fraction of the reaction. product after hydrocarbons of both lower and higher volatility than the Ci fraction have been removed from said prod uct. The object of my invention is to present a method whereby vinylacetylene may be recovered from a complex hydrocarbon mixture containing the same and also containing butenes-2 and any or all of the other C4 acetylenes, diolefins, clens or parains generally encountered in petroleum conversion processes.

Vinylacetylene has value as a base for synthetic rubber, drying oils, and resins, and-is much in demand at the present time. I have discovered that the recovery of vinylacetylene from a mixed aliphatic C4 hydrocarbon stream presents a somewhat unusuai problem which is very diilicult of solution because oi' the following facts: (1) A relatively small diiierential exists in the boiling points between butenes-2, vlnylacetylene, ethylacetylene and bi-acetylene. (2) A minimum boiling point azeotrope exists between vinylacetylene and butenes-2. (3)- A minimum boiling point azeotrope exists between ethylacetylene and bu, tenes-2.

For reference purposes, Table I below shows normal boiling points and normal volatilities of the significant C4 hydrocarbons.

1Normal volatility as here used is donned as the vapor pressure i' the particular hydrocarbons at 41.2 F. divided by the vapor pmfi vinylacetylene at 41.2' F.'(14.7 pounds per square inch l so u I have discovered that the previously mentioned azeotrope between butenes-2 and vinylacetylene is oi the minimum boiling point type: that is, the normal boiling point of the azeotrope is lower than that oi either butenes-2 or vinylacetylene. My invention takes advantage of this phenomenon by providing for the distillation of the butenes-2 vinylacetylene azeotr'ope from the other C4 acetylenes. I have also discovered that various solvents will absorb vinylacetylene in preterence to any C4 dioleilns, oletlns, or paraiilns, and

VI have utilized this fact to eii'ect a recovery of vinylacetylene from admixture with C4 dioleilns. oleiins. and parailins. One advantage of my invention is that the removal of vinylacetylene from a C4 system facilitates the purication ot certain other individual C4 hydrocarbons. For example, in certain butadiene puriiication processes, the final fractionation is made between 1,3 butadiene and butenes-2. It vinylacetylene is present in the system, the formation of the butenes-2 vinylacetylene azeotrope will make the butadiene puriflcation more difficult, because the volatility of the azeotrope is higher than the volatility of butenes-2. Another advantage of my invention is that it makes possible the recovery o'f vinylacetylene from a C4 hydrocarbon mixture by the use of conventional petroleum processing equipment, and requires only conventional heating and cooling media. Still another advantage oi' my invention is that it makes possible the production of acetylene-free C4 diolefinic, olefinic, and parafilnic hydrocarbons.

The accompanying drawing shows one method for purifying vinylacetylene in accordance with' the present invention. A mixed hydrocarbon stream containing butenes-2 and vinylacetylene and comprising any other C4 acetylenes, dioleilns, olens, or paraiilns, is charged via line 4 to the conventional type iractionator I. The vinylacetylenebutenes-Z azeotrope and most of the C4 hydrocarbons are removed overhead while substantially all of the other C4 acetylenes and any C hydrocarbons present are removed as bottom product. However, this separation is possible only ii the butenes-2 are present in the iractionator in that quantity required for the formation of 4the vinylacetylene-butenes-2 azeotrope but not in excess. Since ethyl acetylene and butenes-2 also form an azeotrope of the minimum boiling ppint type. itis necessary -to limit the amount of butenes-2 pres- A ent to that required to form the more volatile vinylacetylene-butenes-2 azeotrope. Ethylacetylene forms an azeotrope with butene-2 (low boiling) when there is 9.5 per cent ethylacetylene present. Ethylacetylene forms an azeotrope with butene-2 (hish' boiling) when there is 25.5 per cent ethyiacetylene present. Thus the quantity o f butenes-2 remaining after all oi the vinylacetylene has combined with the butenes-Z to form an azeotrope must be quite small in order to prevent formation of the ethylacetylene-butenes2 azeotrope. If too large a quantity of butenes2 is '4 present it will tend to force the ethylacetylene out the top of th'e tower thus preventing subsequent recovery of pure vinylacetylene. The overhead product from fractionator l is then charged via line 'I to the absorber tower 2 wherein vinylacetylene is removed by selective solvent extraction.

ation zone. If the feed stream contains too large a percentage of butenes2 it will be necessary to remove a portion of these butenes2 in order to prevent formation of an areotrope between ethylacetylene and the butenes2. The excess of butenes-2 may be removed by any suitable method.

Among the various selective solvents which will absorb vinylacetylene in preference to C4 dioleflns, olefins and paraiiins, are: phenol, phenol plus water, acetone, acetone plus water, dimethylformamide, furfural, furfural plus water, furfuryl alcohol, and methyl levulinate. Any selective solvent which dissolves butadiene in preference to butenes or butenes in preference to butanes should prove satisfactory. For purposes of this discussion, a selective solvent composed of furfural containing a small amount of dissolved water say four weight percent will be used since it is a preferred solvent. Table II shows the relative volatilities at a pressure of 65 pounds per square inch' absolute, in this selective solvent, of the C4 hydrocarbons which may be passed to the absorbing unit.

'The absorber tower 2 is, in eii'ect, a two section extractiva distillation tower, the uppersection of which acts as an absorber for. vinylacetylene while the bottom section of the tower acts as a stripper to remove the other C4 hydrocarbons which are absorbed to some extent in the top section of the tower. The overhead product from the absorber tower 2. leaving vla line Il, is a substantially acetylenes-free stream of C4 hydrocarbons, andgnay be further processed for the recovery of individual components if desired. Any Ca or lighter hydrocarbons retained in the feed to the absorber tower 2 will pass overhead and be removed with the overhead product. Rich' solvent leaves absorber tower 2 as the bottoms product, and is charged via line I2 to the solvent stripper 3, wherein vinylacetylene is removed as overhead product while the lean or denuded solvent is returned, after suitable cooling, via line I 3 to the top of the absorber tower 2. It may be desirable to carry out the stripping of thevinylacetylenerich solvent under low pressure (refrigerated) casacca means. or in th'e presence of a diluting stripping means in order to reduce hazards and prevent such undesirable reactions as polymerization, etc.

Suitable materials for diluting are such inert hy- 5 drocarbons as propane, pentane or olefins depending on the ultimate use of the vinylacetylene.

The process of my invention makes readily possible the production of vinylacetylene having a purity of at least 95% or higher up to practically 100%, depending upon the wish of the operator.

The pressure maintained on the fractional distillation column will usually be that required to enable the use of ordinary plant cooling water for condensing the reflux. and therefore will usually be at least about 60 pounds per square inch absolute, varying upward therefrom to say 100 pounds or higher. Use of pressures below 60 pounds is not ordinarily feasible because of excessive refrigeration requirements for condensing the tower reux. The furfural extractive distillation tower and the stripper operating pressure range will usually be of' the same order as that of the fractional distillation tower. In general increase in pressure decreases the selectivity of the solvent for vinylacetylene. Under certain conditions it may be desirable to use refrigeration for condensing the reflux in the extlractive distillation tower `and stripper tower to prevent the occurrence of undesirable reactions. a

The azeotrope between butenes2 and vinylacetylene boils below butenes2 but above butadiene. The C4 hydrocarbonslare taken overhead with the vinylacetylene-butenes2 azeotrope. In other words, the out is made at such a point that substantially all of the ethylacetylene and the higher boiling components of the feed appear in the bottoms while virtually all of the isobutane. isobutylene, butadiene, butene-l and a substantial part of the n-butane go overhead in admixture with the vinylacetylene-butenes2 azeotrope. There is virtually no butenes2 taken on from the bottom of the column since it was consumed in the formation of the vinylacetylenebutenes2 azeotrope. It will be understood that with the complex C4 mixture usually encountered many unpredictable and complicating factors may aect the theory and result. Thus there is the possibility of the formation of other azeotropes, binary and ternary. For example it is now known that butadiene forms an azeotrope with normal butane. However it has been defi- Nnitely ascertained that a following of the teachings and principles set out herein will enable the worker in the art to duplicate the results disclosed, namely to separate pure or substantially pure vinylacetylene from any complex aliphatic C4 hydrocarbon stream containing the same which may be encountered.

'I'hus my invention depends upon the discovery that by bringing about the formation of the butenes2 vinylacetylene azeotrope the volatility of vinylacetylene can be so increased from its normal value to a value above that of butenes2 that essentially complete separation of all the vinylacetylene from the other C4 acetylenes is assured without necessitating use of special equipment or operations, and further upon the discovery that vinylacetylene can be preferentlally dissolved in a selective solvent away from the butenes2 and the other hydrocarbons in the fractionator overhead which commonly includes butadiene.

While the vinylacetylene-containing C4 stream treated by the process of my invention will usually contain other aliphatic C4 hydrocarbons such as butadiene, butene-l, butenes-Z, normal butane, isobutane and isobutylene each in proportionssubstantially greater than the vinyl-- acetylene, my invention is not limited to such a stream but is applicable to streams containing a. much larger relative proportion of vinylacetylene and less o r practically no butadiene, butene-l, butenes-2, normal butane, isobutane, or isobutylene.

From the foregoing. it will be seen that the present invention is based upon the discovery that minimum-boiling azeotropes are formed not only between vinylacetylene and butenes-2 but also between the other C4 acetylenes and buf tenes-2. Furthermore, it will be seen that the present invention accomplishes the removal of vinylacetylene substantially A uncontaminated with other C4 acetylenes by providing inthe fractionation zone an amount of butenes-Z sufcient to form minimum-boiling azeotropes with all of the vinyl-acetylene present in the feed but not in a substantial excess of this amount. By operating in accordance with the present invention, any other C4 acetylenes go out the bottom while the vinylacetylene is selectively taken overhead in the form of its azeotropes with butenes-Z. If desired, the feed stream may be preliminarily given a solvent extraction to concentrate the Criactylenes where the butenes-2 are present in too great a` quantity. Then the correct amount of butenes-Z based on the vinylacetylene content would be added to the butnes-Z free stream thus obtained and the re-` sulting mixture would be passed to tower I.

It is to be understood that the foregoing illusi terms and spirit of the appended claims.

I claim: f

1. The 'process of recovering vinylacetylene in concentrated form from a C4 hydrocarbon stream containing the same and other aliphatic`C4 hydrocarbons which comprises iractionally distilling said stream while maintaining in the fractionation zone butenes-2 in suillcient amount to form a minimum boiling point azeotrope with vinyl'- acetylene and virtually no excess butenes-2, recovering overhead this azeotrope between said vinylacetylene and said butenes-Z. subjecting the overhead fraction to selective solvent extraction and thereby selectively dissolving the vinylacetylene in the selective solvent, and strippinl the rich solvent to recover concentrated vinylacetylene as the product of the process.

2. The process of recovering vinylacetylene in concentrated form from a C4 hydrocarbon stream containing the same and other more saturated C4 hydrocarbons including isobutane, isobutylens.

butadiene, baume-1, normal butane and butenes-2, at least one of said other more saturated C4 hydrocarbons being present in quantity substantially greater than the proportion oi' vinyl-Y acetylene, and also containing substantial proportions of other C4 acetylenes which comprises fractionally distilling said stream in the presence oi butenes-Z in amount just suillcient to form a minimum boiling point azeotrope with the vinylacetylene present, recovering an overhead conlsisting of an azeotrope of said butenes-Z, and said vinylacetylene in admixture with a substantial proportion of said other more saturated C4 hydrocarbons, subjecting the overhead fraction to extractive distillation in the presence of a solvent selective for vinylacetylene in preference to more saturated C4 hydrocarbons and thereby selectively dissolving the vinylacetylene in the selective solvent while allowing said other more saturated C4 hydrocarbons to pass through undissolved, and stripping the rich solvent to recover concentrated vinylacetylene as the product of the process.

3. The process oflrecovering vinylacetylene in concentrated form from a C4 hydrocarbon stream containing the same and other more saturated C4 hydrocarbons including isobutane, isobutylene,

butadiene, butene-l, normal butane and butenes-2, at least one oi said other more saturated l C4 hydrocarbons being present in quantity substantially greater than the amount o! vinylacetylene, and also containing s. substantial proportion of at least one other C4 acetylene which comprises fractionally distilling said stream in the presence of butenes-2 in amount just sufdcient to form a minimum boiling azeotrope with the vinylacetylene present, recovering an, overhead consisting of an azeotrope of said butenes-2 and said vinylacetylene in admixture with a substantial proportion of said other. more saturated C4 hydrocarbons including substantially all oi saidl butadiene and butene-l, subjecting the overhead fraction to extractive distillation in the presencei of a solvent selective for vinylacetylene in preference to more saturated C4 hydrocarbons and thereby selectively dissolving they vinylacetylene in the selective solvent while allowing said other more saturated C4 hydrocarbons to pass through undissolved, and stripping the rich solvent to recover concentrated vinylacetylene as the product oi the process.

4. The process oi' claim 1 wherein said solvent is furfural.

5. The process of claim 1 wherein said solvent is iurfural plus 4 weight per cent of water.

6. The process` of claim 2 wherein said solventr is furiural.

'1. The process oi claim 3 wherein said solvent 

